7-Nitro-3,4-dihydro-2,2-dimethyl-3,4-epoxy-2H-benzo[b]pyran (0.48 g, the preparation of which is described in Example 3 of U.K. Pat. No. 1,548,221), ethyl 4-aminobutyrate hydrochloride (0.34 g) and sodium hydroxide pellets (0.08 g) were refluxed in ethanol (50 ml) for 12 hours. Filtration and evaporation and chromatography on a chromatotron (2 mm silica gel HF254, gradient elution with pentane-ethyl acetate) gave recovered epoxide (0.20 g) and trans-4-(3-carbethoxypropylamino)-7-nitro-2,2-dimethyl-2H-benzo[b]pyran-3-ol (0.21 g) as a gum, which was used as such in Example 10.
